Electrosurgical resection is a procedure in which damaged, diseased or enlarged tissue is removed with an electrosurgical probe. An example is transurethral resection of the prostate (TURP), in which prostate tissue is removed by means of an electrosurgical (electrocautery) probe, for example, a cutting loop that is passed through the urethra by means of a resectoscope. This procedure has served as the historical treatment of benign prostate hypertrophy (BPH) and prostatitus. Another example is endometrial ablation, which is an electrosurgical alternative treatment to hysterectomy in women with menorrhagia (abnormal uterine bleeding). In this case, an electrosurgical probe is passed through the vagina by means of a hysteroscope.
Ablation and resection are electrosurgical effects accomplished by applying a highly damped radio frequency (RF) current to the tissue through an electrode in the form of an active (+) tip of an electrosurgical probe, from which the RF current flows to a second ground (−) electrode. As it passes through tissue from the active tip to the ground electrode, the RF current cuts and/or coagulates the tissue, depending on power and wave length combinations. RF electrosurgical probes are typically equipped with a telescope so that the active tip of the probe is in direct view of the surgeon at all times. RF electrosurgical probes, and particularly their active tips, are available in a number of shapes, sizes, and types, including but not limited to loop (wire), ball tip, roller tip, barrel, cone, point, knife, flat band, coagulating, and punctate electrodes. Examples of a loop electrode suitable for use in TURP and other procedures are represented in FIGS. 1 and 2. In each of FIGS. 1 and 2, RF electrosurgical probes 10 are shown equipped with a loop electrode 12 in which an electrically-conductive U-shaped wire loop is supported between a pair of electrically-conductive arms.
Conventional RF electrosurgical probes (RF probes), such as those commonly used in urological and hysteroscopic resection procedures, are said to be monopolar even though two electrodes are required to complete the RF circuit. FIG. 1 is representative of a monopolar RF probe 10, with the loop electrode 12 of the probe 10 being the active (+) tip of the probe 10, while the other electrode 14 is represented as a patient plate that serves as the ground (−) pole of the RF circuit. The patient plate is typically located on the patients hip or buttocks. The monopolar designation comes from the fact that the probe 10 itself has a single pole. In the circuit described above, the human body becomes a resistive conductor in the negative side of the circuit. This circuit has been used for over eighty years.
Irrigating solutions serve as a coolant for the active tips of RF probes as well as a distention medium to inflate the bladder in urology and the uterus is hysteroscopy. Because the body is not an ideal conductor, it has long been conventional wisdom that only non-conductive irrigation solutions can be used during RF resection procedures, since conductive solutions would dissipate the RF energy and greatly reduce the tissue effect or cutting performance of the probe. In FIG. 1, the use of a non-conductive irrigation solution promotes the flow of RF current from the loop electrode 12, through the tissue 16 being cut, and through the remainder of the human body between the electrode 12 and the ground electrode 14. A commonly-used non-conductive solution is sorbitol (C6H14O6). The concern of non-conductive irrigation solutions is that they are absorbed by the body during surgery (a process known as intravasation). Too much intravasation during a procedure can result in numerous complications including heat failure, brain damage, etc. The concern for intravasation forces the surgeon to hurry the procedure so as to limit the time that the open wounds are exposed to intravasation of fluids.
Normal saline has no adverse effect on the human body and can even be injected intravenously, and therefore does not have the aforementioned drawbacks of non-conductive irrigation fluids. However, saline is conductive and therefore cannot be used with conventional monopolar RF probes. For example, with reference again to FIG. 1, the use of a conductive irrigation solution causes the RF current to dissipate into the solution from the loop electrode 12, instead of being focused through the tissue 16 to the ground electrode 14.
The desire to use saline irrigation fluids has driven new technology referred to as bipolar electrodes, an example of which is represented in FIG. 2. It is believed that prior art “bipolar” electrodes have often involved simply energizing the metal frame 18 of an otherwise conventional monopolar RF probe 10, such that the metal frame 18 becomes the ground (−) pole of the RF circuit. This in effect moves the ground electrode 14, previously a patient plate located at the patient's hip or buttocks, to a position close enough to the active (+) electrode tip (loop 12) of the probe 10 so that the RF current flows a short distance from the loop 12, through the conductive (saline) solution, to the metal frame 18 of the probe 10. In this manner, loss of RF current by dissipation to the conductive saline irrigation fluid is reduced, and the desired tissue effect or cutting performance of the probe 10 is not significantly degraded.
The use of saline irrigation fluids with bipolar electrodes has been relatively successful, yet has distinct disadvantages. First, using the metal frame 18 of the probe 10 energizes the entire resectoscope or hysteroscope, which could result in burns to the surrounding tissue or the surgeon. For this reason, a patient plate (FIG. 1) may be used in addition to energizing the metal frame 18 to avoid this potential safety issue. Another disadvantage arises because electrical current always searches for the easiest path to ground. In the prior art, because the entire frame 18 of the probe 10 is ground, the RF current does not have a well-focused point to search for.